1. Field of the Invention
This invention relates generally to oilfield drilling operations and more particularly to simultaneous drilling and casing of wellbores with a drill string utilizing a liner or casing and a steerable drilling assembly.
2. Background of the Art
In conventional manner, oil wells (wellbores) are drilled with a drill string having a drilling assembly with a drill it at its bottom, and a tubular member (either a jointed pipe or coiled tubing) attached to the drilling assembly that extends to the surface. Once a section of the well has been drilled, the drill string is retrieved to the surface and a casing, which extends to the surface, is set in the well to protect the open hole. A liner is hung below the upper casing using a liner hanger connection device, which usually includes two threaded connections at its bottom. The liner is connected to the outer thread. The inner threaded connection is used to connect a string inside that liner, which string extends below the liner hanger. The next section of the wellbore is drilled below the first liner and this procedure is repeated until the telescopically declining diameter wellbore is drilled to the desired depth. Such drilling methods require tripping the entire drill string out of the wellbore for lining each telescopic section of the wellbore.
Wellbores are sometimes drilled wherein the liner itself is employed to carry the drilling assembly. The drilling assembly used for such operations includes a drill bit at the bottom to drill a pilot (small diameter) hole followed by an underreamer which enlarges the pilot hole to a size greater than the outer dimensions of the liner. The drilling assembly is retrievably attached to the liner bottom and can be retrieved without retrieving the liner.
To drill curved holes, the underreamer drilling assemblies typically use a bent housing (also referenced to as a xe2x80x9cbent subxe2x80x9d) whose attitude is fixed either at the surface or downhole, which attitude defines the drilling direction. Such drill strings are sometimes unable to provide precision directional drilling.
The present invention provides apparatus and method for drilling wellbores with liners which allow relatively precise directional control. This invention further provides apparatus and method wherein an expandable liner may be used during the drilling process, which liner can ne expanded while the drilling assembly is retrieved to the surface, thereby avoiding a secondary operation required to expand the expandable liner.
The present invention provides apparatus and method for drilling a wellbore with a drilling assembly wherein a pilot wellbore section is drilled with a bit which section is enlarged by a trailing underreamer to the desired size. The drilling assembly includes one or more steering sections between the underreamer and the drill bit are utilized for maintaining and changing the drilling direction. Each steering section includes a plurality of independently adjustable force application devices on a non-rotating sleeve. The drilling assembly is retrievably attached at its upper end to a liner that will be set in the wellbore once at least a section of the wellbore has been drilled. The liner may be any suitable tubing including a expandable liner. If an expandable liner is used, then an expansion device disposed above the underreamer is utilized to expand the liner during retrieval of the drilling assembly to the surface.
The independently adjustable force application devices provide for a relatively precise control of the direction of drilling. A control unit on the surface and/or in the drilling assembly controls the force applied by each of the force application devices in accordance with programmed instructions and/or commands provided from surface. One or more sensors in the drilling assembly and at the surface provide information about various parameters of interest, including the tool face of the drilling assembly, force applied by each application device, and position of the drilling assembly. The control unit includes an electronic processor (computer, microprocessors and the like) and controls the operation of the force application device, at least in part, in response to or as a function of one or more parameters, of interest, thereby controlling and/or maintaining the drilling direction along a desired path.
Examples of the more important features of the invention thus have been summarized rather broadly in order that the detailed description thereof that follows may be better understood, and in order that the contributions to the art may be appreciated. There are, of course, additional features of the invention that will be described hereinafter and which will form the subject of the claims appended hereto.